How does the electricity market work?

[agricola]

So far, it looks like there are

1) Generators
2) Distributors
3) Suppliers

Generators generate electricity
Distributors send it down the wires
Suppliers do jack shit but charge £83 of the total bill since the previous two both generate and supply

Doesnt make sense. The generators and distributors are supplying electricity to my home. What do the suppliers claim to be doing?